1. Field of the Invention
Catalytically active compositions for use in plating metal on a nonconductive substrate by electroless deposition.
2. Description of the Prior ARt
U.S. Pat. No. 3,011,920 (Shipley) describes a process in which a colloidal solution is prepared by mixing an aqueous acid solution of palladium chloride with an aqueous acid solution of stannous chloride and optionally including a tin salt such as sodium stannate. This is purported to produce a lyophilic colloid which, after acceleration with an acid or alkaline solution such as hydrochloric acid or sodium hydroxide provides a sensitizing layer for the subsequent electroless plating of a metal such as copper.
U.S. Pat. No. 3,672,923 (Zeblisky) describes solid compositions dilutable to optically clear sensitizing solutions for electroless plating. These solutions are prepared by combining a dilute solution of a noble metal salt in hydrochloric acid with a hydrochloric acid solution of a stannous salt such as stannous chloride dihydrate. The mixture is heated and then subsequently cooled and evaporated to dryness under vacuum to constant weight. The solid composition, as described, may then be reconstituted in hydrochloric acid to provide an active sensitizing solution.
Nathan Feldstein, "Reliability in Printed Circuitry Metalization -- A case for Improved Catalyzing Systems", Plating, June 1973. In the Feldstein article it is recognized that the inclusion of halide salts improves the stability of catalytic sensitizer solutions.
U.S. Pat. No. 3,904,792, Gulla et al, issued Sept. 9, 1975. This patent discloses the advantages of using excess halide ions, in concentrations of at least 0.2 moles/liter in excess of the other chloride ion components, such as furnished by stannous and palladium chloride solutions.